A card reader includes a card interface, and one of the pins of the card interface is selected to decide the state of the card interface. The card reader further includes a control circuit to detect the logic state of the selected pin. If the logic state is a first one, the control circuit decides the card interface is enabled; otherwise, if the logic state is a second one, the control circuit decides the card interface is disabled. In some embodiments, a switch is connected between the selected pin and a power supply or a ground terminal, to be switched by a control signal to enable or disable the card interface.